1. Field of the Invention
The present invention relates in general to a display apparatus, and more particularly, to a computer monitor which can display a clear moving picture and has a lengthened life span.
2. Description of the Related Art
Generally, as shown in FIG. 5, a display apparatus comprises a plurality of signal amplifiers 56 and 57 amplifying a picture signal from a computer 50, a display part 53 displaying the picture signal amplified by signal amplifiers 56 and 57, a flyback (fly back or fly-back) transformer (FBT) 65 generating an auto brightness limit (ABL) signal for controlling a magnitude of a gain of the picture signal by adjusting an electric current supplied to signal amplifiers 56 and 57 and supplying a high voltage (G1 voltage) to an electron gun, and a controller 60 generating vertical and horizontal blanking signals, according to the picture signal and vertical and horizontal synchronous signals received from computer 50.
As shown in FIG. 6, the display apparatus outputs a horizontal waveform signal through the signal amplifiers 56 and 57 and a vertical waveform signal with the G1 voltage. The gain of the horizontal waveform output voltage controls a contrast of the display apparatus. The higher the gain of the horizontal waveform output voltage is, the sharper the contrast is. Oppositely, the lower the gain of the horizontal waveform output voltage is, the weaker the contrast is. Brightness is controlled according to a difference between a horizontal cutoff voltage and the vertical G1 voltage. The smaller the voltage difference is, the higher the brightness is. Oppositely, the greater the voltage difference is, the lower the brightness is.
In comparison with a television set, the display apparatus is located relatively close to a user when in use and operated at a relatively high frequency. Thus, in order to lengthen a life span of the display apparatus and to protect the user""s eyes, the contrast and the brightness of the display apparatus are generally set up with a relatively low value, compared with the television.
Accordingly, when the display apparatus is used to display a moving picture, it is neither clear nor bright, because of the low values of the contrast and brightness. Recently, various moving pictures are being supplied to a user, as the Internet becomes more popular. Thus, a user wants to watch clear and bright moving pictures, similar to the television.
Accordingly, a method has been provided which can display clear and bright moving pictures by raising a gain of a horizontal waveform output voltage so as to enhance the contrast or by raising the G1 voltage so as to enhance the brightness. However, if the gain of the horizontal waveform output voltage or the G1 voltage is raised, a circuit of the display apparatus is subjected to an overload, thereby shortening the life span of the display apparatus.
Accordingly, the present invention has been made keeping in mind the above-described shortcoming and user""s need, and an object of the present invention is to provide a display apparatus which can display a clear and bright moving picture without shortening a life span of the display apparatus.
This and other objects of the present invention may be accomplished by the provision of a display apparatus having a display part, comprising an amplifying part amplifying an inputted picture signal and transmitting it to the display part; a clock signal generating part generating a clock signal in synchronization with at least one of the vertical and horizontal synchronous signals transmitted together with the inputted picture signal; and a controller controlling the amplifying part to adjust an amplification rate so that brightness is alternately changed within a predetermined limit according to at least one of the periods of the horizontal and vertical synchronous signals, synchronizing with the clock signal generated from the clock signal generating part.
Preferably, the display apparatus further comprises an electron gun emitting electron beams for displaying the inputted picture signal on the display part, and a FBT supplying high voltage to the electron gun; wherein the controller adjusts the output voltage from the FBT so that brightness is alternately changed within a predetermined limit in synchronization with the clock signal generated from the clock signal generating part.
Desirably, the controller adjusts the amplification rate of the amplifying part and voltage from the FBT in order to alternately change the brightness and contrast of the display part, according to the period of horizontal synchronous signal synchronizing with the clock signal generated from the clock signal generating part.
Preferably, the clock signal generating part includes a first signal generator generating a clock signal according to the horizontal synchronous signal of the picture signal, and a second signal generator generating a clock signal according to one of the vertical and horizontal synchronous signals of the picture signal.
The controller can adjust the contrast of the picture signal by increasing and decreasing the amplification rate of the amplifying part according to the period of the horizontal synchronous signal, synchronizing with the clock signal generated from the first signal generator.
The controller raises the voltage and increases the brightness for one period of the vertical synchronous signal synchronizing with the clock signal generated from the second signal generator, and lowers the voltage and decreases the brightness for the next period thereof.
The controller lowers the amplification rate of the amplifying part and makes the contrast weak for one period of the vertical synchronous signal, and raises the amplification rate of the amplifying part and makes the contrast sharp for the next period thereof.
The controller receives the clock signals generated from the first and second signal generators, and alternately increases and decreases the amplification rate of the amplifying part according to the period of the horizontal synchronous signal along with the voltage.
The controller raises the voltage so as to increase the brightness of the picture signal for every even turn of the period of the horizontal synchronous signal in one period of the vertical synchronous signal, and lowers the voltage so as to decrease the brightness of the picture signal for every even turn of the period of the horizontal synchronous signal in the next period of the vertical synchronous signal.
The controller decreases the amplification rate of the amplifying part so as to make the contrast for every even turn of the period of the horizontal synchronous signal in one period of the vertical synchronous signal, and increases the amplification rate of the amplifying part so as to make the contrast sharp for every even turn of the period of the horizontal synchronous signal in the next period of the vertical synchronous signal.
The controller respectively raises and increases the voltage and the amplification rate of the amplifying part so as to increase the brightness and to make the contrast of the picture signal sharp for every even turn of the period of the horizontal synchronous signal in one period of the vertical synchronous signal, and respectively lowers and decreases the voltage and the amplification rate of the amplifying part so as to decrease the brightness and to make the contrast of the picture signal weak for every even turn of the period of the horizontal synchronous signal in the next period of the vertical synchronous signal.
The display apparatus further comprises a selection part for selecting a moving picture mode; wherein the controller operates the signal generating part when the moving picture mode is selected through the selection part.